The present invention relates to an overload-preventing device that is applied to a winch such as a chain block, a manual hoist, etc.,
The applicant previously proposed an overload-preventing device for a winch, which is disclosed in Japanese Patent Publication No. 17994 of 1989. The overload-preventing device includes, as shown in FIG. 7, a drive shaft b that transmits a rotating force to a load sheave a; a pressure-receiving member c that is fixed at the drive shaft b; a pressing drive member g that is screwed with the drive shaft b so as to advance and retreat and presses and rotates the pressure receiving member c via a reverse rotation preventing wheel d that is fitted to the outside of the pressure receiving member c and a pair of friction members e and f that are disposed at both sides thereof; a rotation drive member j that is not permitted to rotate with respect to the pressing drive member g but is movable in the axial direction, has an outer circumferential surface of a truncated cone member h, the diameter of which is reduced toward the side of the pressure-receiving member c, and an inner circumferential surface following the outer circumferential surface of the truncated cone member h, and is outwardly fitted so that it is brought into frictional contact with the tip end side face in the axial direction of the truncated cone member h and pressing drive member g; wherein the truncated cone member is pressed toward the pressing drive member by a truncated cone pressing member. In the device, if the rotation torque of the rotation drive member, which is necessary for winding-up, exceeds the friction force given between the rotation drive member and the truncated cone portion or the pressing drive member by the truncated cone pressing member, the rotation drive member runs idly, whereby it is possible to prevent an overload applied to the rotation drive member from being added to the drive shaft, and influences due to wearing resulting from the friction can be reduced by making the contacted surface between the rotation drive member and the truncated cone member conical surface.
However, in a prior art construction, when an overload-preventing device operates due to an overload resulting from an accidental impact in the process of unwinding a load, the rotation drive member slips with respect to the truncated cone member and pressing drive member. Therefore, there was a fear that the operation of the winch would be disabled. Therefore, a load is hung dangling from a chain suspended from a load sheave, wherein there is a fear that the load cannot be unload or unwound. Also, where an overload is applied due to a load crumble after the load is tightened by a lever hoist, a rope cannot be slackened, wherein there is a fear that the rope must be cut off.
The present invention was developed to solve the abovementioned themes.
The present invention applies to a winch that includes a drive shaft that transmits a rotating force to a load sheave; a pressure-receiving member that is fixed at the drive shaft; a pressing drive member that is screwed with the drive shaft so as to advance and retreat, and presses and rotates the pressure receiving member via a reverse rotation preventing wheel that is fitted to the outside of the pressure receiving member and via a pair of friction members that are disposed at both sides thereof; a truncated cone member, the diameter of which is reduced toward the side of the pressure-receiving member, that is not permitted to rotate with respect to the pressing drive member but is movable in the axial direction; and a rotation drive member, having an inner circumferential surface following the outer circumferential surface of the truncated cone member, which is outwardly fitted so that it is brought into frictional contact with the outer circumferential surface of the truncated cone member and the tip end side face in the axial direction of the pressing drive member; wherein the truncated cone member is pressed toward the pressing drive member by a truncated cone pressing member.
And, the overload-preventing device of a winch according to the invention is featured in that, in the winch as described above, an accommodation hole for accommodating a movable piece is formed in the abovementioned rotation drive member so as to open in the contact surface with the pressing drive member, the movable piece is retained so as to come out of and sink in the accommodation hole but not to move in the circumferential direction, the abovementioned movable piece is pressed to the side of the pressing drive member by the movable piece pressing member, an engagement groove having a depth in which a part of the movable piece has infiltrated is formed on the same radius as that of the accommodation hole on the contact surface of the pressing drive member, the engagement groove has a length by which the movable piece can move in the circumferential direction, the end portion at the winding-up side is formed so that it becomes shallow toward the winding-up side to become continuous on the contact surface, and the end portion at the unwinding side is formed on the fitting plane on which the movable piece cannot move in the unwinding direction.
Also, the overload-preventing device of a winch according to the invention is featured in that, in the winch as described above, an accommodation hole for accommodating a movable piece is formed in the pressing drive member so as to open in the contact surface with the rotation drive member, the movable piece is retained so as to come out of and sink in the accommodation hole but not to move in the circumferential direction, the abovementioned movable piece is pressed to the side of the rotation drive member by the movable piece pressing member, an engagement groove having a depth in which a part of the movable piece is absorbed is formed on the same radius as that of the accommodation hole on the contact surface of the rotation drive member, the engagement groove has a length by which the movable piece can move in the circumferential direction, the end portion at the unwinding side is formed so that it becomes shallow toward the unwinding side to become continuous on the contact surface, and the end portion at the winding-up side is formed on the fitting plane on which the movable piece cannot move in the winding-up direction.
Also, in addition to any one of the above-mentioned constructions, the abovementioned pressing drive member has a flange portion formed at the side of the pressure-receiving member, and has a boss portion extending and formed in the direction opposed to the pressure-receiving member. The abovementioned truncated cone member is spline-fitted to the base end portion of the boss portion, and the above-mentioned truncated cone pressing member is fitted to the outer side of the intermediate portion thereof and is positioned by a nut. It is preferable that the flange portion of the abovementioned pressing drive member is constructed so that one end thereof is brought into contact with the abovementioned friction member while the other end thereof is brought into contact with the abovementioned rotation drive member.
As described in detail, according to a chain block of the invention, in the case where the rotation drive member rotates in the unwinding direction, the rolling member that is pressed by the movable piece pressing member is brought into contact with the fitting plane of the engagement groove, wherein since rotation of the rotation drive member is transmitted to the pressing drive member, unwinding operation of the drive shaft is enabled in an overloaded state. Therefore, a situation will not occur where an overload is suspended or a rope used for the tightening of a crumbled load is cut off.
Furthermore, in the case where the rotation drive member is caused to rotate in the winding-up direction, the rolling member is pushed up onto the frictional plane along the inclined plane, wherein a rotation force of the rotation drive member is not transmitted to the pressing drive member via the rolling member. Therefore, the slipping motion of the rotation drive member with respect to the pressing drive member is not hindered even in an overloaded state, and the overload-preventing function is not hindered.